RESUMO
Translation initiation plays a critical role in the regulation of cell growth and tumorigenesis. We report here that inhibiting translation initiation through induction of eIF2α phosphorylation by small-molecular-weight compounds restricts the availability of the eIF2.GTP.Met-tRNAi ternary complex and abrogates the proliferation of cancer cells in vitro and tumor growth in vivo. Restricting the availability of the ternary complex preferentially down-regulates the expression of growth-promoting proteins and up-regulates the expression of ER stress response genes in cancer cells as well as in tumors excised from either animal models of human cancer or cancer patients. These findings provide the first direct evidence for translational control of gene-specific expression by small molecules in vivo and indicate that translation initiation factors are bona fide targets for development of mechanism-specific anti-cancer agents.
Assuntos
Antineoplásicos/farmacologia , Cromanos/farmacologia , Clotrimazol/farmacologia , Ácido Eicosapentaenoico/farmacologia , Iniciação Traducional da Cadeia Peptídica/efeitos dos fármacos , Tiazolidinedionas/farmacologia , Animais , Pontos de Checagem do Ciclo Celular/efeitos dos fármacos , Linhagem Celular Tumoral , Proliferação de Células/efeitos dos fármacos , Ciclina D1/biossíntese , Modelos Animais de Doenças , Fator de Iniciação 2 em Eucariotos/metabolismo , Feminino , Humanos , Camundongos , Camundongos Endogâmicos DBA , Fosforilação/efeitos dos fármacos , Biossíntese de Proteínas , Distribuição Aleatória , Troglitazona , Ensaios Antitumorais Modelo de XenoenxertoRESUMO
The cyclin-dependent kinase inhibitor p27(Kip1) plays a critical role in regulating entry into and exit from the cell cycle. Post-transcriptional regulation of p27(Kip1) expression is of significant interest. The embryonic lethal abnormal vision (ELAV)-like RNA-binding protein HuR is thought be important for the translation of p27(Kip1), however, different reports attributed diametrically opposite roles to HuR. We report here an alternative mechanism wherein HuR regulates stability of the p27(Kip1) mRNA. Specifically, human and mouse p27(Kip1) mRNAs interact with HuR protein through multiple U-rich elements in both 5' and 3' untranslated regions (UTR). These interactions, which occur in vitro and in vivo, stabilize p27(Kip1) mRNA and play a critical role in its accumulation. Deleting HuR binding sites or knocking down HuR expression destabilizes p27(Kip1) mRNA and reduces its accumulation. We also identified a CT repeat in the 5' UTR of full-length p27(Kip1) mRNA isoforms that interact with a approximately 41-kDa protein and represses p27(Kip1) expression. This CT-rich element and diffuse elements in the 3' UTR regulate post-transcriptional expression of p27(Kip1) at the level of translation. This is the first demonstration that HuR-dependent mRNA stability and HuR-independent mRNA translation plays a critical role in the regulation of post-transcriptional p27(Kip1) expression.
Assuntos
Antígenos de Superfície/metabolismo , Inibidor de Quinase Dependente de Ciclina p27/genética , Regulação da Expressão Gênica , Processamento Pós-Transcricional do RNA , RNA Mensageiro/genética , Proteínas de Ligação a RNA/metabolismo , Regiões 3' não Traduzidas , Animais , Ciclo Celular , Proteínas ELAV , Proteína Semelhante a ELAV 1 , Humanos , Camundongos , Células NIH 3T3RESUMO
BACKGROUND: Chaotic organization, abnormal leakiness, and structural instability are characteristics of tumor vessels. However, morphologic events of vascular remodeling in relation to tumor growth are not sufficiently studied yet. METHODS: By using the rat rhabdomyosarcoma tumor model vascular morphogenesis was studied by light and electron microscopy and immunohistochemistry in relation to tumor regions such as tumor surrounding (TSZ), marginal (TMZ), intermediate (TIZ), and center (TCZ) zones. RESULTS: The analyses revealed that blood vessels of TSZ display a regular ultrastructure, whereas blood vessels of TMZ showed a chaotic organization and unstable structure with a diffuse or even lacking basal lamina, and missing or irregular assembled periendothelial cells. In contrast, blood vessels of TIZ and TCZ exhibited a more or less stabilized vessel structure with increased diameter. Correspondingly, normal assembly of alpha-smooth-muscle-actin (alpha-SMA)-positive cells into the vessel wall was observed in blood vessels of TSZ, TIZ, and TCZ. Also, Ang1 immunostaining was strongest in large vessels of TIZ and TCZ, whereas Ang2 staining was prominent in small vessels of TIZ. Tie2 staining was detectable in small and large vessels of all tumor zones. Immunostaining for alpha(v)beta(3)-integrin was strongest in small vessels of TMZ, whereas large vessels of TIZ and TCZ were almost negative. CONCLUSIONS: The results indicate a zone-specific remodeling of tumor blood vessels by stabilization of vessels in TIZ and TCZ, whereas small vessels of these zones obviously undergo regression leading to tumor necrosis. Thus, a better understanding of vascular remodeling and stabilization in tumors would enable new strategies in tumor therapy and imaging.
